distribution of methyl bromide in soils treated for nematode control in replant vineyards
TRANSCRIPT
Pestic. Sci. 1974, 5 , 259-269
Distribution of Methyl Bromide in Soils Treated for Nematode Control in Replant Vineyards
Nabil Abdalla, Dewey J. Raski, Bert Lear and Richard V. Schmitt
Department of MematoIogy, University of Califbrnia, Davis, California 95616, U.S.A. (Revised manuscript received February 1974 and accepted 19 February 1974)
Methyl bromide was applied with and without polyethylene covers at rates of 337, 449, 673 and 898 kg/ha to replant vineyard soils to control plant parasitic nematodes. Distribution of the gas in the soil atmosphere at different depths was measured by gas chromatography. Higher doses, low soil moisture and deeper placement of methyl bromide resulted in more rapid soil penetration and higher concentrations of the gas at the deeper soil levels. Placement of methyl bromide in the soil at 0.76-0.81 m without polyethylene cover resulted in gas distribution at concentrations sufficient for nematode kill as deep as 2.44 m.
1. Introduction Use of methyl bromide as a soil fumigant for the control of plant diseases and nematodes is well established, mostly on shallow-rooted crops.'-3 The material is generally applied either by chisels set at 0.1-0.2 m depths and the soil immediately covered with polyethylene sheetings or by releasing the gas between the soil surface and a cover.4 These techniques were less successful for the control of oak root fungus, Armillaria mellea, nematodes and virus in vineyards and orchards because of the deep distribution of roots and pathogens in the soil.
Some of the early trials with methyl bromide against Xiphinema index for control of fanleaf virus5 were unsuccessful. Deeper placement of methyl bromide gave much better results at 1.83 m6 and has since been used in other trials at 0.61-0.76 m depths against root-knot and other nematode^.^^^ Trials involving deep placement have raised other questions including correlation of lethal dose of methyl bromide against various species of nematodes, particularly root-knot, effect of soil type and other soil conditions on efficacy, best methods of application and the optimum rate. Van Gundy et a1.8 reported Meloidogyne incognita, X . index and a Dorylaimus sp. in soil exposed to fiowing methyl bromide (600 pl/litre) were neither motile nor infective after 48 h expo- sure. Laboratory experiments' have shown exposures for 24 h of 500-550 and 600- 650 pl methyl bromide/litre are required to kill X . index and M . incognita respectively. Munnecke et a1.2,10 indicated that increasing the rate of application and decreasing the soil moisture content resulted in more rapid diffusion of methyl bromide deeper in the soil.
The objects of this study were to determine: (1) The effect of rate and method of application on the distribution and concentra-
tions of methyl bromide in soil under different field conditions. 259
260 N. Abdalla et al.
(2) The effect of soil type, soil moisture and soil temperature on the distribution of
(3) The efficacy of the methods used on nematode control. methyl bromide at different soil depths.
2. Materials and methods 2.1. Preparation of soil Five experimental field plots were used in this study. In all plots the soil was prepared before fumigation by ripping in two directions by sub-soiling chisels to a depth of about 0.76 m then disced and roller packed to smooth the surface. Specific procedures used for soil preparation will be described for each plot.
2.2. Application of methyl bromide
Methyl bromide was applied as a liquid with chisels set at 1.68 m spacing and 0.51- 0.81 m deep on a commercial tractor-drawn machine. When methyl bromide was applied with cover, polyethylene sheeting was laid down by the same machine immediately behind the chisel applicators. The sheeting was 4 m wide, 25 pm thick overlapped 0.61 m on the previously treated strip resulting in a 3.4 m wide treatment with each pass of the equipment.
2.3. Sampling of methyl bromide
The concentration of methyl bromide in the soil atmosphere was determined by gas chromatography of samples drawn from different depths utilising the technique of Kolbezen and Abu-El-Hag." Each sampling probe consisted of four stainless steel tubes (0.3, 1.2, 1.8,2.4 m long) fastened to a 2.6 m long channel iron. In placing the probes in each plot, care was taken to site them between the chisels. Analysis of the samples was carried out immediately in the field where the gas chromatograph was kept in a camper truck that was driven to the different plots. Good agreement (to within 4.3%) was normally observed between replicate samples taken at the same depth.
2.4. Gas chromatography
The chromatographic conditions were as follows. Instrument: Varian Aerograph Model 1200 with flame ionisation detector, and 6-port gas sampling valve with 0.5 ml sample loop. Column: Stainless steel, 0.6 m x 6 mm i.d. Packing: 25% Dow Corning high vacuum grease on Chromosorb W, 100-120 mesh. Flow rates: Hydrogen 30 ml/ min; Carrier gas (nitrogen) 30 ml/min; Air 300 ml/min. Retention time: 26 s.
The samples were analysed in duplicate and the peak height was used as the criterion for concentration. Standard concentrations of methyl bromide in aira were used to calibrate the gas chromatograph before running each set of samples.
2.5. Bioassay
The nematicidal effectiveness of methyl bromide was evaluated by taking soil samples at various depths. For root-knot nematode assay, gall counts were made on roots of
a Prepared by Dr M. J. Kolbezen, Department of Plant Pathology, University of California, Riverside, U.S.A.
TA
BL
E
1. M
ethy
l bro
mid
e co
ncen
trat
ion
in s
oil a
tmos
pher
e: e
ffec
t of
dosa
ge a
nd f
allo
w v
s. c
ultiv
atio
n. P
lot
I
Soil
Sam
ple"
m
oist
ure
at
dept
h (m
) tr
eatm
ent (
%)
Fallo
w a
rea
0.30
1.
22
1.83
2.
44
Suda
n pl
antin
g 0.
30
1.22
1.
83
2.44
7.6
9.9
14.1
13
.6
6.8
7.4
5.4
6.6
Met
hyl b
rom
ide
conc
entr
atio
n* in
soi
l atm
osph
ere
(plil
itre)
App
licat
ion
rate
C
App
licat
ion
rate
C
App
licat
ion
rate
C
App
licat
ion
rate
C
337
kg/h
a 44
9 kg
/ha
673
kg/h
a 89
8 kg
/ha
Day
s af
ter a
pplic
atio
n D
ays
afte
r ap
plic
atio
n D
ays
afte
r app
licat
ion
Day
s af
ter
appl
icat
ion
14
81
4
4 6
11
14
4 6
11
14
14
81
4
A
r \
/
/
\/
./
- fl
\I
*
-
,-
2100
80
0 10
0 50
11
00
500
50
30
700
300
70
60
3100
80
0 15
0 10
0 40
50
2300
11
00
200
1750
14
50
500
200
1800
13
00
200
100
4400
19
00
1400
70
0 19
50
2000
10
00
400
1700
15
00
900
600
2100
19
00
900
500
900
3000
26
00
1600
30
0 80
0 80
0 45
0 16
50
1600
10
00
700
3000
30
00
1950
14
00
800
4000
36
00
2300
2700
10
00
200
50
1350
85
0 20
0 10
0 13
00
1000
20
0 10
0 76
00
2700
12
00
600
4800
25
00
900
250
4050
28
50
1000
50
0 38
00
3300
13
00
700
5300
27
50
1400
60
0 15
00
1700
80
0 20
0 50
00
3800
17
00
1200
37
00
3500
17
00
1200
32
00
6000
35
00
2000
30
0 70
0 60
0 30
0 40
00
3400
18
00
1300
19
00
2100
18
00
1600
12
00
5000
40
00
3000
Mec
hani
cal a
naly
sis
of s
oil:
(mea
n fo
r al
l dep
ths)
21.
5% c
lay,
25.
5% s
ilt a
nd 5
3% s
and.
Met
hyl b
rom
ide
was
app
lied
0.61
m d
eep
unde
r po
lyet
hyle
ne c
over
, whi
ch w
as re
mov
ed a
fter
11
days
. * E
ach
valu
e is
the
mea
n fr
om tw
o pr
obes
.
262 N. Abdalla et al.
tomato seedlings grown for 30 days in 400 ml aliquots of each soil sample. For other genera of nematodes involved, another 400 ml aliquot of each soil sample was wet sieved and counts of motile and non-motile nematodes made directly from the sievings.
2.6. Description of field plots
2.6.1. Plot I Location : St Helena, Napa County, California. Nematodes involved : A'. index and Criconemoides xenoplax. Soil type : Bale fine sandy clay loam ; for properties see Table 1. Vines (2.02 ha) were pulled in the spring of 197O.One-half the area was planted with Sudan grass to reduce soil moisture, the other half was left fallow. In September 1970 the Sudan grass was cut and the soil prepared for fumigation. The plot was divided into four sections across the grass and fallow areas. Single replicate treatments of methyl bromide (337, 449, 673 and 898 kg/ha) were applied 0.61 m deep under poly- ethylene cover in plots 17 m wide extending across both the fallow and Sudan-treated areas. Gas samples were taken at intervals up to 14 days from treatments (Table 1). St George No. 2 cuttings were planted in 1971 and the soil was sampled November 1970 and May 1972 for nematodes.
2.6.2. Plot 11 Location : Delano, Kern County, California (Block 21 F). Nematodes involved : M . incognita, Meloidogyne jauanica, Xiphenima americanum and Criconemoides sp. Soil type: Hanford sandy loam (Table 2). Emperor grapes were pulled in the spring of 1971 and the plot planted to Sudan grass. In the autumn of 1971 the grass was cutand the soil prepared for fumigation. On 14 October 1971, the following treatments were applied at 0.51 m depth: 337 and 449 kg methyl bromide/ha to areas 23.3 x 192 m under
TABLE 2. Methyl bromide concentration in soil atmosphere: effect of polyethylene cover. Plot I1
Methyl bromide concentration* in soil atmosphere (Ml/litre)
Application rate' Application rate' 449 kg/ha with coverd 449 kg/ha no cover
r -- c . Sample" Soil Days after application Days after application depth moistureat I -, 7
(m) treatment ('A 1 3 11 19 1 3 11 19
0.30 2.4 6050 2600 700 100 1200 700 100 0 1.22 3.4 3700 3600 900 250 1650 1300 200 50 1.83 - 1400 2600 1100 400 400 500 250 50 2.44 3.8 150 1400 1300 600 150' 200' 250' 150'
Mechanical analysis of soil: (mean for all depths) 8% clay, 18% silt, 74% sand. * Average reading from 4 probes.
Methyl bromide was applied 0.51 m deep. Cover removed after 11 days. Some liver Meloidogyne incognita found 3 months after treatment.
Methyl bromide in vineyard soils 263
polyethylene cover, and 449 kg/ha (6.8 x 192 m) without cover. Gas readings were taken up to 19 days after application (Table 2). On 27 January 1972, soil samples were taken for nematode assay.
2.6.3. Plot 111 Location : Arvin, Kern County, California. Nematodes involved : M . incognita, Pratyl- enchus sp., ParatyIenchus sp. Soil type: San Emigdio sandy loam (Table 3). Cardinal grapes were pulled in the winter of 1970 and the soil was prepared in the autumn of 1971. Methyl bromide (449 kg/ha) was applied 0.61 m deep to an area 44.6 x 198 m with poly- ethylene cover, and to 14.9 x 198 m without cover. In the uncovered area, a light water
TABLE 3. Methyl bromide concentration in soil atmosphere: effect of water or polyethylene seal after treatment. Plot 111
Methyl bromide concentrationb in soil atmosphere (plilitre)
Application rate" Application rate' Application ratec 449 kg/ha 449 kg/ha 449 kglha water seal no cover polyethylene cover"
c .
Days after application Days after application Days after application Sample" I < 7 ,
depth(m) 1 3 16 1 3 16 1 3 16
0.30 2100 800 100 2200 700 50 6350 2700 400 1.22 2900 1500 150 2500 1600 150 3850 3500 700 1.83 1000 1350 200 500 1200 200 1500 2350 900
150 700 250 100 550 250 200 1300 900 2.44
Soil temperature ("C): 17, 18.3 and 20 at 0.30,0.91 and 1.52 m depths, respectively; soil moisture: 4,8.3 and 6.4% at 0.30,0.91 and 1.52mdepths,respectively;mechanicalanalysis (mean of all depths): 13 % clay, 24% silt and 63 % sand.
Average of 3 sampling probes from treatments without cover and from 4 probes from the covered treatment.
Methyl bromide was applied 0.61 m deep. Cover removed after 16 days.
seal was applied to half the area using water sprayed from tank truck driven over it. Gas samples were taken up to 16 days after fumigation. Soil samples for nematode bio- assay were taken 6 months after treatment.
2.6.4. Plot IV Location : Delano, Kern County, California (Block 21-A). Nematodes involved : M . javanica, X. index, X. americanum, ParatyIenchus sp. and Pratylenchus sp. Soil type: Hanford sandy loam (Table 4). White Malaga grapes were pulled in autumn 1971 and the soil prepared in June 1972. The area was divided into 4 sections, each 14.9 x 186 m and methyl bromide was applied 0.76-0.81 m deep at the following rates: 337,449 and 673 kg/ha, all without polyethylene covering. A similar section of the plot was left untreated. Gas readings were taken up to 14 days after treatment.
TAB
LE
4. M
ethy
l bro
mid
e co
ncen
tratio
n in
soi
l atm
osph
ere:
effe
ct o
f do
sage
at d
eep
plac
emen
t of
the
fum
igan
t. Pl
ot I
V
Met
hyl b
rom
ide
conc
entr
atio
nb in
soil
atm
osph
ere
(pl/l
itre)
~~
~~~
~~~
App
licat
ion
rate
c A
pplic
atio
n ra
te'
App
licat
ion
rate
' 33
7 kg
/ha
449
kglh
a 67
3 kg
/ha
I
T
. So
il So
il D
ays a
fter a
pplic
atio
n D
ays
afte
r app
licat
ion
Day
s af
ter a
pplic
atio
n Sa
mpl
e"
moi
stur
e at
te
mpe
ratu
re ,
1,
-
,,
Y
dept
h (m
) tr
eatm
ent (
%)
("C
) 1
3 7
14
1 3
7 14
1
3 7
14
0.30
2.
8 30
28
50
600
180
10
4950
11
50
250
50
7250
12
00
400
50
1.22
5.
9 24
15
50
1950
70
0 15
0 10
oO
2200
85
0 15
0 38
00
4050
15
00
400
700
3000
17
00
600
1.83
7.
3 22
.2
550
1100
80
0 30
0 20
0 95
0 85
0 30
0 2.
44
10.4
21
50
40
0 60
0 30
0 30
40
0 50
0 25
0 30
80
0 13
00
700
(I M
echa
nica
l ana
lysi
s of
soil:
(mea
n of
all
dept
hs) 1
4.5
% cl
ay, 2
4.5
% si
lt an
d 62
% s
and.
A
vera
ge fr
om 3
pro
bes.
M
ethy
l bro
mid
e w
as a
pplie
d at
0.7
6-0.
81
m d
epth
with
out
cove
r.
TA
BL
E
5. M
ethy
l bro
mid
e co
ncen
trat
ion
in s
oil a
tmos
pher
e: e
ffec
t of
cove
r. Pl
ot V
Met
hyl b
rom
ide
conc
entr
atio
nb in
soi
l atm
osph
ere
(pl/l
itre)
L
I
7
Met
hyl b
rom
ide
(449
kg/
ha) a
pplie
d'
Met
hyl b
rom
ide
(449
kgi
ha) a
pplie
d'
with
pol
yeth
ylen
e cov
erd
with
out c
over
,
Y
Soil
Soil
Day
s af
ter a
pplic
atio
n So
il D
ays
afte
r ap
plic
atio
n Sa
mpl
e"
tem
pera
ture
m
oist
ure
at ,
moi
stur
e at
,
. de
pth
(m)
("C
) tr
eatm
ent ('b
1
3 7
trea
tmen
t (%
) 1
3 7 -
Surf
ace'
66
00
300
450
-
-
0.07
6 8.
9 7.
5 71
00
1100
10
0 13
.3
550'
25of
20
0 0.
15
11.1
6.
5 62
00
3100
12
00
8.7
2300
13
00
1 200
0.
30
13.3
2.
3 85
00
4400
29
00
3.9
4100
21
50
1800
0.
61
15.6
2.
1 94
00
5400
37
00
3.6
4900
25
00
2300
Mec
hani
cal a
naly
sis
of s
oil:
(mea
n of
all
dept
hs)
8%
cla
y, 1
8% s
ilt a
nd 7
4% s
and.
A
vera
ge re
adin
g fr
om 4
sam
plin
g pr
obes
exc
ept w
here
oth
erw
ise
stat
ed.
Cov
er re
mov
ed a
fter
7 d
ays.
Rea
ding
s fr
om o
ne g
as sa
mpl
ing
prob
e.
' Met
hyl b
rom
ide
was
app
lied
at 0
.76-
0.81
m d
epth
.
' Ave
rage
of
4 ga
s sa
mpl
es fr
om a
ir b
etw
een
the
poly
ethy
lene
cov
er a
nd s
oil s
urfa
ce.
266 N. Abdalla et at.
2.6.5. Plot V
This plot was designed to study the distribution and nematicidal activity of methyl bromide in the first 0.3 m of the treated soil. Location: Block 21-F, adjacent to Plot 11. Nematodes involved: same as in Plot 11. Soil type: Hanford sandy loam. Grapes were pulled in the spring of 1972. In November 1972 the soil was prepared and the area was divided into two parts (28.6 x 265 m each) and methyl bromide (449 kg/ha) applied to one part under polyethylene cover while the second part was without cover. The gas sampling probes were 0.61 m long, with four tubes fastened at 0.076,0.15,0.39 and 0.61 m along the channel iron. In the case of the polyethylene-covered treatment additional gas samples were taken from the atmosphere between the cover and the soil surface.
Due to heavy rain at the time of application, the soil moisture was very high especially at the first 0.15 m of soil and it eliminated the gas samples from most of the sampling tubes at the 0.076 m depth. Samples were taken up to 7 days after application (Table 5).
3. Results 3.1. Plot I The gas readings (Table 1) indicate that increasing methyl bromide dose resulted in more rapid diffusion and higher concentrations of the gas at greater depths of the soil. Planting Sudan grass reduced the soil moisture below that of simple fallow, especially at depths of 1.2-1.8 and 1.8-2.4 m (Table 1). This resulted in more rapid movement of the gas deeper in the soil.
Gas concentrations in soil atmosphere required to eliminate nematodes (as indicated from laboratory experiment^)^ were reached at all the treatments at all the soil depths sampled. These gas readings are correlated with nematode kill as shown in the soil samples taken 8 months after application. All the samples from treated soil were free of 2'. index, and samples from untreated soil had X . index at all depths with an average of 32lvine site.
3.2. Plot I1 Gas readings indicate that methyl bromide gas followed the same diffusion pattern as in Plot I. Methyl bromide (449 kg/ha) applied without a cover gave lower gas concentra- tion at all depths than at this rate with polyethylene cover, especially at the 2.4 m depth where the gas did not reach the concentration required for nematode kill. This is corre- lated with the finding of root-knot galls on indicator plant from one of the soil samples at that depth while samples from 0.3-1.8 m were free from nematodes. Rates of 337 and 449 kg methyl bromide/ha under polyethylene cover gave good nematode control since no nematodes were recovered from soil samples from 0.3-2.4 m depths. Soil samples from untreated area had root-knot nematodes in all depths with an average of 37 gal/ 400 ml of soil.
3.3. Plot I11
This plot was designed to study further the behaviour of methyl bromide applied without a polyethylene cover. Lower concentrations (Table 3) were found at all IeveIs in the soil
Methyl bromide in vineyard soils 267
compared with the section with polyethylene cover but reached the concentrations required for nematode kill. When 449 kg/ha of methyl bromide were applied without cover the gas reached the required lethal concentration 3 days after application, but due to sampling time lag it is not known for how long the desired concentration was maintained. Application of the water seal did not aid much in holding the gas in the soil. However, the amount of water used did not wet the soil beyond the top 0.025 rn of the soil surface.
Soil samples taken 5 months after treatment were free from nematode in all samples from all treatments at 0.3-2.4 m depths. Untreated check areas showed 2 out of 6 samp- ling locations were free from nematodes which indicates uneven distribution of nema- todes in this plot.
3.4. Plot IV
Plots I1 and I l l showed methyl bromide applied without a cover gave promising nema- tode control, but dosages were marginal at the 2.4 m level and there was also a rapid decline in concentrations at the 0.3 m level. Deeper placement of the fumigant at 0.76-0.81 m was tested here as a possible method to overcome these problems. Results (Table 4) showed that high concentrations were maintained at the 0.3 m level and the distribution pattern was similar to that found when methyl bromide was applied under cover (i.e. 24 h after application the highest gas concentration was found at the 0.3 m depth followed by the 1.2, 1.8 and 2.4 m depths). Dosages required for nematode kill were achieved at all depths at all 3 rates. These results must be compared with nematode assay in soil samples which will be taken later.
3.5. Plot v There is concern that the required dosage of methyl bromide may not be achieved in the shallow layers between the 0.3 m depth and the surface. This trial was designed to obtain data from that zone. Due to heavy rain during application and sampling the soil moisture increased greatly, especially at the first 0.15 m depth in the uncovered area (Table 5). This resulted in loss of the gas samples from most of the sampling probes at the 0.076-0. I5 m level; water was withdrawn in the sampling syringes instead of gas. However, except for gas samples taken at the 0.075 m depth in the uncovered area, methyl bromide gas reached concentrations sufficient for nematode control. The effect of porosity of the polyethylene cover to methyl bromide is apparent in Table 5. The gas concentration in the air beneath the 25 pm polyethylene cover decreased rapidly over the 7 day sampling period which indicates that considerable gas was lost by diffusion to the air through the cover.
4. Discussion
The high-rate, deep-placement application of methyl bromide has been successful thus far in the control of plant-parasitic nematodes in replant vineyards.
Four main methods of applying methyl bromide to the soil were tested in this study:
(1) Application of methyl bromide at 0.61 m depth under polyethylene cover. (2) Application of methyl bromide at 0.61 m depth without cover.
268 N. Abdalla et al.
(3) Application of methyl bromide at 0.61 m depth with water seal. (4) Deeper placement of methyl bromide at 0.76-0.8 1 m depth without cover.
The pattern of diffusion of methyl bromide gas in soil is affected by the application method used. When method (1) was used, higher gas concentrations were found at lesser soil depths (0.3-1.2 m) reaching maximum concentration in that level one day after application, followed by sharp decline over the sampling period especially at the 0.3 m level. This rapid decline may be accounted for by considerable loss of gas by diffusion to the air through the polyethylene sheeting.2j12 Gas concentration at the lower depths (1.8-2.4 m) reached the maximum 3-4 days after application followed by gradual decline over the sampling time. Approximately one week after application, the gas concentration rapidly declined at all depths indicating that the gas was diffusing to other areas of the soil. By the end of the sampling period (2-3 weeks) the highest gas concentration was at the 2.4 m depth and decreasing at the 1.8, 1.2 and 0.3 m, respec- tively. When the polyethylene cover was eliminated (Method 2) a similar pattern of dif- fusion was found, except that the gas reached maximum concentration at the 1.2 m depth one day after application followed by lower concentration at the 0.3, 1.8 and 2.4 m depths. This indicated a rapid escape of the gas from the 0.3 m level to the air.
Applying water seal to the soil surface following the injection of the fumigant resulted in a slightly higher gas concentration but did not change the diffusion pattern. However, further study is needed to determine whether sufficient water applied here was sufficient to give a good seal. When methyl bromide was injected at the 0.764.81 m without cover, the gas diffusion pattern was similar to that obtained when Method 1 was used. This suggests that deeper placement of the fumigant reduced loss to the air, though the two application depths were not compared in the same trial.
When 449 kg methyl bromide/ha was applied at 0.51 m depth without cover (Plot II), gas concentrations at the 2.4 m depth were below that required for nematode kill. This suggests that the chemical was not placed deep enough under the conditions of this plot. However, this treatment was tested only once, and further investigation is needed.
Increasing rates of methyl bromide resulted in more rapid soil penetration, and higher concentrations of the gas at the deeper levels. Deep placement of methyl bromide at 0.76-0.81 m depth without cover looks promising for reducing cost because the poly- ethylene sheets are expensive and pose problems in their use and disposal. Because of the variable conditions of each plot tested, no experiment was an exact duplicate of another. However, it was noticed that in drier soil and with higher soil temperature, gas penetration into the soil was greater, and higher concentration of the gas was found deeper in the soil. It is difficult to draw conclusions regarding the effect of soil type on gas distribution, since the soil types were very similar in all the tested plots. However, results from laboratory experiments9 and other reports2 indicate that gas penetration is greatest in coarse textured soils, decreasing as the soil texture becomes finer. The beha- viour of methyl bromide within the first 0.3 m of soil indicates that a concentration high enough for nematode kill was maintained over the required exposure time. However, due to the limiting weather condition that occurred during this experiment, further study is needed. The efficacy of methyl bromide for nematode control demonstrated by bio- assay tests is promising. Continued observations of the growth and yieIds in these
Methyl bromide in vineyard soils 269
replanted vineyards will be taken over a period of years. Only then will it be possible to make a complete evaluation of these treatments and their practicality as an economic control method.
References 1. Darby, J. F. PI. Dis. Reptr 1961, 45, 58. 2. Munnecke, D. E.; Kolbezen, M. J.; Stolzy, L. H. First f n t . Citrus Symp. Proc. 1969,3,1273. 3. Thomason, I. J. PI. Dis. Reptr 1959, 43, 580. 4. Hague, N. G. M.; Lubatti, 0. F.; Page, A. B. P. Hort. Res. 1964,3, 84. 5 . Raski, D. J.; Schmitt, R. V. PI. Dis. Reptr 1972, 56, 1031. 6. O'Bannon, J. H.; Bistline, F. W. PI. Dis. Reptr 1969, 53, 799. 7. Raski, D. J.; Schmitt, R. V.; Luvisi, D. A.; Kissler, J. J. PI. Dis. Reptr 1973,57, 619. 8. Van Gundy, S. D.; Munnecke, D. E.; Bricker, J.; Minteer, R. Phytopathology 1972,62,191. 9. Abdalla, N. Ph. D. Diss. 1973, University of California, Davis.
10. Munnecke, D. E.; Wilbur, W. D.; Kolbezen, M. J. Phytopaihobgy 1970, 60, 992. 11. Kolbezen, M. J.; Abu-El-Haj, F. J. Pesfic. Sci. 1972, 2, 73. 12. Lear, B. Personal communication. 1973.